OPA445AP datasheet(10/25 Pages) TI

10 / 25 page

OPA445

SBOS156B − MARCH 1987 − REVISED APRIL 2008

www.ti.com

SAFE OPERATING AREA

Stress on the output transistors is determined both by the

output current and by the output voltage across the

conducting output transistors, VS − VO. The power

dissipated by the output transistor is equal to the product

of the output current and the voltage across the conducting

transistor, VS − VO. The Safe Operating Area (SOA curve,

Figure 6 through Figure 10) illustrates the permissible

range of voltage and current. The curves shown represent

devices soldered to a printed circuit board (PCB) with no

heat sink. Increasing printed circuit trace area or the use

of a heat sink (TO-99 package) can significantly reduce

thermal resistance (

q ), resulting in increased output

current for a given output voltage (see Figure 11,

Figure 12, and the Heat Sink section).

The safe output current decreases as VS − VO increases.

Output short-circuits are a very demanding case for SOA.

A short-circuit to ground forces the full power supply

voltage (V+ or V−) across the conducting transistor and

produces a typical output current of 25mA. With

±40V

power supplies, this creates an internal dissipation of 1W.

This

exceeds

the

maximum

rating

and

not

recommended. If operation in this region is unavoidable,

a heat sink is required. For further insight on SOA, consult

Application Bulletin SBOA022 (available for download at

www.ti.com).

S| − |VO|(V)

100

A =25_ C

A = 120_ C

A =85_ C

A +[(|VS| − |VO|) IO ×θJA] ≤ TJ (max)

JA = 100_ C/W

J (max) = 125_ C

100

0.1

Figure 6. DIP-8 Safe Operating Area

S| − |VO|(V)

100

0.1

A =25_ C

A =85_ C

A = 125_ C

A +[(|VS| − |VO|) IO ×θJA] ≤ TJ (max)

JA = 200_ C/W (No Heat−Sink)

J (max) = 150_ C

NOTE: Simple clip−on heat−sinks can

reduce

θ by as much as 50_C/W.

Figure 7. TO-99 Safe Operating Area

S| − |VO|(V)

100

0.1

A =85_ C

A = 120_ C

A +[(|VS| − |VO|) IO ×θJA] ≤

J (max)

JA = 150_ C/W

J (max) = 125_ C

A =25_ C

Figure 8. SO-8 (non PowerPAD) Safe Operating

Area

110

S| − |VO|(V)

100

0.1

A =25_ C

A =85_ C

A =120_ C

A +[(|VS| − |VO|) IO ×θJA] ≤ TJ (max)

JA =96_ C/W

J (max) = 125_ C

Figure 9. SO-8 PowerPAD Safe Operating Area

(no heat-spreader, no airflow)

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